1. Field of the Invention
The present invention relates to a method of forming a resist pattern and to an exposure device, and in particular, to a method of forming a resist pattern and an exposure device which are based on an exposure technique using a KrF excimer laser as a light source in the production of a semiconductor integrated circuit.
2. Description of the Related Art
Conventionally, in manufacturing a semiconductor integrated circuit, in order to form a finer pattern, a KrF exposure technique has been mainly used, in which deep UV light having a wavelength of 248 nm is emitted as exposure light from a KrF excimer laser light source. In this KrF exposure technique, it is possible to form a patter of about 0.2 μm.
Japanese Patent Application Laid-Open (JP-A) No. 11-119443 discloses, in such a KrF exposure technique, a technique in which a fine pattern of about 0.2 μm or less is obtained by shrinking the resist pattern (e.g., shrinking the internal diameter of the hole pattern formed at the resist) by baking the resist at a temperature which is higher than the usual baking which is carried out in order to remove the residual solvent and the residual moisture which remain after the resist pattern has been formed. In accordance with this technique, it is possible to form a pattern of about 0.1 μm or less, which exceeds the resolution limit of the KrF exposure technique.
The method disclosed in the aforementioned JP-A-11-119443 is suited to the formation of an extremely fine pattern for which the size (dimension) of a feature (e.g., the diameter of a contact hole, the width of an embedded wiring, or the like) is less than or equal to the resolution limit of the KrF exposure technique. However, for a relatively large pattern whose feature dimension is greater than the resolution limit of the KrF exposure technique, the pattern after baking deteriorates, and thus, this method is not preferable.
For example, as illustrated in FIG. 10A, when holes (a contact hole pattern) of a diameter of about 0.25 μm and holes (a contact hole pattern) of a diameter of about 0.5 μm are formed in a resist and the resist is baked for 60 seconds at around 135° C., as illustrated in FIG. 10B, the side walls at the holes (the contact hole pattern) of a diameter of about 0.25 μm do not deform and only the diameter decreases such that holes of a diameter of about 0.1 μm are formed. However, at the holes (the contact hole pattern) having a diameter of about 0.5 μm, the resist side walls forming the pattern curve towards the centers of the holes, such that deformed holes whose smallest diameter is 0.35 μm are formed.
When a resist having holes of such configurations is used as a mask in the etching process which is carried out later, the portions corresponding to the peaks of the convex shapes of the resist are gradually removed as the film to be processed, which is the layer therebeneath, is etched. In addition, the resist side walls are curved toward the centers of the holes and the smallest diameter thereat is 0.35 μm. Therefore, considering that the diameter of the bottom surface of the hole which is nearer to the surface of the film to be processed is greater than 0.35 μm and that the film to be processed can be somewhat side-etched at the border region at the time of etching, a hole of a diameter much larger than the desired diameter is formed in the film to be processed. This tendency becomes marked particularly when the diameter of the resist pattern before baking is greater than 0.5 μm.